The golf ball has a multiplicity of dimples on its surface. The dimples causes turbulence of air flows around the golf ball when flying, thereby creating a turbulent separated flow. This phenomenon is referred to as “creation of turbulence”, and this creation of turbulence shifts backward an air separation point from the golf ball, resulting in reducing drag (force acting in a direction of repulsion against a flying direction). The creation of turbulence increasingly enlarges a deviation between an upper air separation point and a lower air separation point of the golf ball due to a backspin, thereby augmenting a dynamic lift acting on the golf ball. Accordingly, well-designed dimples create better turbulence of the air flows and produce a longer carry.
In recent years, a technology has been also developed to enhance aerodynamic characteristics by polishing the surface of the golf ball in addition to contriving a shape of a dimple. For instance, Japanese Patent Application Laid-Open Publication No. 2004-14783 proposes a method for applying a blast treatment over the surface of a coating layer in order to reduce the drag when the golf ball flies. Another instance is that Japanese Patent Application Laid-Open Publication No. 2007-260317 proposes a method for applying a rough surface work to a bottom surface of the dimple in order to reduce the drag and improve the dynamic lift when the golf ball flies. Still another instance is that Japanese Patent Application Laid-Open Publication No. 2002-369896 proposes a method for forming micro dimples each having a diameter equal to or smaller than ½ as small as a diameter of the dimple formed by the blast treatment in order to extend the carry of the golf ball. Yet another instance is that Japanese Translation of PCT International Application Publication No. 2014-520654 proposes a method for providing roughness to the surface by polishing the surface of the golf ball in order to have an influence on aerodynamic performance of the golf ball.
A long carry is demanded of a driver shot, and, however, when an extra dynamic lift is caused by the influence of the dimples, a flying golf ball has a hopping trajectory, resulting a possibility that the carry shortens. Although a variety of examinations have hitherto been made not to generate the hopping trajectory in designing the dimples, this problem still remains unsolved, and it is desirable to develop a method for improving the aerodynamic performance of the golf ball not confined to the design of the dimple.